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Table 3 Multivariable logistic regression analyses for postoperative AKI according to increase in serum chloride levels (Cl−)

From: Hyperchloremia and postoperative acute kidney injury: a retrospective analysis of data from the surgical intensive care unit

Group

Variable

Multivariable model 3

Odds ratio (95% CI)

P value**

Entire sample (n = 7991)

Increase in Cl−, mmol L− 1*

 Q1: ≤ 1 mmol L− 1

1

(0.756)

 Q2: 1–3 mmol L− 1

0.84 (0.60, 1.18)

0.316

 Q3: 3–6 mmol L− 1

0.89 (0.66, 1.21)

0.456

 Q4: > 6 mmol L− 1

0.90 (0.66, 1.24)

0.528

Interaction of increase in Cl− with eGFRa

 Increase in Cl−: Q1 * eGFR: ≥ 90

1

(0.297)

 Increase in Cl−: Q2 * eGFR: 60–89

1.04 (0.64, 1.70)

0.867

 Increase in Cl−: Q2 * eGFR: 30–60

0.93 (0.60, 1.44)

0.738

 Increase in Cl−: Q2 * eGFR: < 30

1.02 (0.60, 1.75)

0.934

 Increase in Cl−: Q3 * eGFR: 60–89

0.93 (0.60, 1.44)

0.738

 Increase in Cl−: Q3 * eGFR: 30–60

0.99 (0.63, 1.57)

0.973

 Increase in Cl−: Q3 * eGFR: < 30

1.10 (0.67, 1.80)

0.702

 Increase in Cl−: Q4 * eGFR: 60–89

0.92 (0.58, 1.46)

0.728

 Increase in Cl−: Q4 * eGFR: 30–60

1.51 (0.95, 2.40)

0.084

 Increase in Cl−: Q4 * eGFR: < 30

1.67 (1.01, 2.77)

0.045

 

Four subgroup analysis

Odds ratio (95% CI)

P value***

eGFR ≥ 90 (n = 3437)

Increase in Cl−, mmol L− 1

 Q1: ≤ 1 mmol L− 1

1

(0.739)

 Q2: 1–3 mmol L− 1

0.84 (0.60, 1.19)

0.323

 Q3: 3–6 mmol L− 1

0.90 (0.66, 1.22)

0.491

 Q4: > 6 mmol L− 1

0.90 (0.66, 1.24)

0.529

eGFR < 90 (n = 4554)

Increase in Cl−, mmol L− 1

 Q1: ≤ 1 mmol L− 1

1

(0.023)

 Q2: 1–3 mmol L− 1

0.84 (0.68, 1.05)

0.123

 Q3: 3–6 mmol L− 1

0.88 (0.72, 1.07)

0.195

 Q4: > 6 mmol L− 1

1.16 (0.94, 1.41)

0.164

eGFR < 60 (n = 2201)

Increase in Cl−, mmol L− 1

 Q1: ≤ 1 mmol L− 1

1

 

 Q2: 1–3 mmol L− 1

0.82 (0.61, 1.09)

0.164

 Q3: 3–6 mmol L− 1

0.90 (0.70, 1.17)

0.430

 Q4: > 6 mmol L− 1

1.42 (1.09, 1.84)

0.009

eGFR < 30 (n = 862)

Increase in Cl−, mmol/L

 Q1: ≤1 mmol L− 1

1

(0.068)

 Q2: 1–3 mmol L− 1

0.85 (0.56, 1.28)

0.428

 Q3: 3–6 mmol L− 1

0.94 (0.64, 1.40)

0.775

 Q4: > 6 mmol L− 1

1.48 (1.00, 2.21)

0.053

  1. Covariates with P < 0.2 on univariable analysis (see also Additional file 3) were included in the final multivariable model to adjust for potential confounders. Covariates for multivariable model 3 included preoperative American Society of Anesthesiologists (ASA) score, preoperative estimated glomerular filtration rate (eGFR), NaCl 0.9% and balanced crystalloid infused. The Hosmer-Lemeshow goodness-of-fit test was performed to investigate the fitness of the multivariable logistic regression models, and revealed no indication of lack of fit. Specifically, the Hosmer-Lemeshow statistic and P value, respectively, were 4.38 and 0.821 for the entire sample; 4.44 and 0.823 for the group of patients with eGFR ≥ 90 mL·min− 1·1.73·m− 2; 10.98 and 0.203 for the group of patients with eGFR < 90 mL·min− 1·1.73·m− 2; 11.92 and 0.155 for the group of patients with eGFR < 60 mL·min− 1·1.73·m− 2; 5.29 and 0.726 for the group of patients with eGFR < 30 mL·min− 1·1.73·m− 2
  2. AKI acute kidney disease, CI confidence interval, Cl− serum chloride levels
  3. aPreoperative eGFR (mL·min− 1·1.73·m− 2) was calculated using the Modification of Diet in Renal Disease formula: 186 × (preoperative serum Creatinine)-1.154 × (Age)-0.203 (× 0.742 if female)
  4. *The increase in Cl− was calculated as the difference between the preoperative value and the maximum value noted during postoperative days (PODs) 0–3. The following quartiles were obtained: Q1, 2535 patients (31.7%); Q2, 1593 patients (20.0%); Q3, 2075 patients (26.0%); and Q4, 1788 patients (22.4%)
  5. **P < 0.05 ***P < 0.012 (after Bonferroni correction) were considered to indicate statistical significance
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